1. Technical Field
The present invention relates to cannulas for simultaneously transporting fluids in opposite directions to and from a surgical site. More particularly, the present invention relates to a cannula assembly for simultaneously aspirating and irrigating an ophthalmic surgical site.
2. The Prior Art
In certain ophthalmic surgical procedures, such as extracapsular cataract extraction, it is required that the surgical site be simultaneously irrigated and aspirated. Hand-held cannula assemblies for performing these functions have been commercially available for some time. One such assembly, which is widely used, includes a generally cylindrical handle having concentric steel tubes projecting from its forward end. The inner tube serves as an aspiration cannula and extends into the handle interior where it is soldered to a narrow connection tube which, in turn, connects to a plastic tube. The latter extends out to the rearward end of the handle to a suction device. The outer steel tube serves as the irrigation cannula and has a tapered forward end which contacts and is soldered to a section of the aspiration cannula periphery. An egress opening in a forward tapered section delivers pressurized irrigation fluid to the surgical site from the annular flow space between the two cannulas. Irrigation fluid is delivered axially into this annular flow space from another narrow connection tube which is soldered to the two cannulas and to the aspiration connection tube. The irrigation connection tube receives pressurized irrigation fluid from a plastic tube which extends parallel to the plastic aspiration tube and out through the rearward end of the handle to a source of pressurized fluid. The two narrow connection tubes are difficult to assemble to the rearward end of the cannulas because of the small sizes of the cannulas and the connection tubes. In addition, the soldered joint, wherein both connection tubes communicate axially with respective cannulas, requires one or both of the connection tubes to be bent off-axis in order that each can be properly oriented with respect to its cannulas and soldered in place. This cannula bending and connection tube placement in the cylindrical handle radially enlarges the interior space required for the soldered joint, thereby requiring the handle diameter to be larger than would otherwise be necessary so that the joint may be accommodated. As a general rule, ophthalmic surgeons prefer a smaller diameter handle, both for ease in manipulating the device and for providing maximum visible access to the surgical site.